The present invention relates to a circuit for producing the operating voltages and the horizontal-deflection current for picture-reproducing equipment.
In particular the invention relates to such a circuit for use in equipment comprising a picture tube, a horizontal-deflection circuit including a series combination formed by a deflection capacitor and the horizontal-deflection coils and of a bidirectional switch in parallel with the series combination, a supply circuit supplying energy to the horizontal-deflection circuit, a vertical-deflection circuit, and a power supply providing the high voltage necessary to operate the picture tube and further operating voltages.
Picture tubes of the type employed in television receivers are increasingly being used for other applications. Even the picture tube in a television receiver is used to reproduce not only television pictures but also teletext or videotex information and programmable video games, for example. Picture tubes similar to those in the television receiver are also used in monitors and visual display units for displaying graphs and characters in data processing or office communication systems. The different displays and in particular those having large, monochromatic areas, and sharp boundaries require higher resolution and a reduced flicker. Both can be achieved by increasing the scanning frequencies.
The horizontal-deflection coils and a deflection capacitor form a resonant circuit in which the energy does not oscillate freely, however. The energy is so influenced by a bidirectional electronic switch (such as a thyristor or transistor with a diode connected in inverse parallel) that a horizontal-frequency sawtooth current is obtained. This resonant circuit dissipates electrical energy; the lost energy is periodically resupplied to the circuit by a switch.
The high voltage necessary to operate the picture tube is produced by a high-voltage transformer followed by a voltage-multiplying circuit. The high-voltage transformer is operated at the horizontal scanning rate; to this end, it is connected in parallel with the horizontal-deflection circuit. In general, further voltages required to operate the set are produced by means of the high-voltage transformer, too.
To increase the scanning frequencies, which is necessary for many applications, involves increasing the operating frequency of the high-voltage transformer. In principle, high frequencies are desirable for the operation of the high-voltage transformer, but frequencies above approximately 15-20 kHz should be avoided.